Fix #2223

httplib.h

@@ -10429,6 +10429,13 @@ inline void ClientImpl::set_error_logger(ErrorLogger error_logger) {
 #ifdef CPPHTTPLIB_OPENSSL_SUPPORT
 namespace detail {
 
+inline bool is_ip_address(const std::string &host) {
+  struct in_addr addr4;
+  struct in6_addr addr6;
+  return inet_pton(AF_INET, host.c_str(), &addr4) == 1 ||
+         inet_pton(AF_INET6, host.c_str(), &addr6) == 1;
+}
+
 template <typename U, typename V>
 inline SSL *ssl_new(socket_t sock, SSL_CTX *ctx, std::mutex &ctx_mutex,
                     U SSL_connect_or_accept, V setup) {
@@ -11087,14 +11094,18 @@ inline bool SSLClient::initialize_ssl(Socket &socket, Error &error) {
         return true;
       },
       [&](SSL *ssl2) {
+        // Set SNI only if host is not IP address
+        if (!detail::is_ip_address(host_)) {
 #if defined(OPENSSL_IS_BORINGSSL)
-        SSL_set_tlsext_host_name(ssl2, host_.c_str());
+          SSL_set_tlsext_host_name(ssl2, host_.c_str());
 #else
-        // NOTE: Direct call instead of using the OpenSSL macro to suppress
-        // -Wold-style-cast warning
-        SSL_ctrl(ssl2, SSL_CTRL_SET_TLSEXT_HOSTNAME, TLSEXT_NAMETYPE_host_name,
-                 static_cast<void *>(const_cast<char *>(host_.c_str())));
+          // NOTE: Direct call instead of using the OpenSSL macro to suppress
+          // -Wold-style-cast warning
+          SSL_ctrl(ssl2, SSL_CTRL_SET_TLSEXT_HOSTNAME,
+                   TLSEXT_NAMETYPE_host_name,
+                   static_cast<void *>(const_cast<char *>(host_.c_str())));
 #endif
+        }
         return true;
       });
 

test/test.cc

@@ -7366,6 +7366,48 @@ TEST(KeepAliveTest, SSLClientReconnectionPost) {
   ASSERT_TRUE(result);
   EXPECT_EQ(200, result->status);
 }
+
+TEST(SNI_AutoDetectionTest, SNI_Logic) {
+  {
+    SSLServer svr(SERVER_CERT_FILE, SERVER_PRIVATE_KEY_FILE);
+    ASSERT_TRUE(svr.is_valid());
+
+    svr.Get("/sni", [&](const Request &req, Response &res) {
+      std::string expected;
+      if (req.ssl) {
+        if (const char *sni =
+                SSL_get_servername(req.ssl, TLSEXT_NAMETYPE_host_name)) {
+          expected = sni;
+        }
+      }
+      EXPECT_EQ(expected, req.get_param_value("expected"));
+      res.set_content("ok", "text/plain");
+    });
+
+    auto listen_thread = std::thread([&svr] { svr.listen(HOST, PORT); });
+    auto se = detail::scope_exit([&] {
+      svr.stop();
+      listen_thread.join();
+      ASSERT_FALSE(svr.is_running());
+    });
+
+    svr.wait_until_ready();
+
+    {
+      SSLClient cli("localhost", PORT);
+      cli.enable_server_certificate_verification(false);
+      auto res = cli.Get("/sni?expected=localhost");
+      ASSERT_TRUE(res);
+    }
+
+    {
+      SSLClient cli("::1", PORT);
+      cli.enable_server_certificate_verification(false);
+      auto res = cli.Get("/sni?expected=");
+      ASSERT_TRUE(res);
+    }
+  }
+}
 #endif
 
 TEST(ClientProblemDetectionTest, ContentProvider) {